Photoresponsive Monolayers Containing In-Chain Azobenzene

Azobenzene monolayers on silicon have been prepared by two synthetic methods: (1) chemisorption of triethoxysilanes, and (2) acylation of amine-functionalized self-assembled monolayers with acid chloride derivatives. A series of films were prepared with different methylene spacer lengths and different terminal end groups (pentyl vs hydrogen). The resulting films were characterized using water contact angles, X-ray photoelectron spectroscopy, attenuated total reflectance infrared spectroscopy, and X-ray reflectivity (XR). Despite evidence for successful attachment of azobenzene to the surfaces, film thicknesses as determined by XR suggest uniform, but incomplete, monolayers. Irradiation of the films with 354 nm light effected a decrease in the water contact angle. The largest photoinduced changes in contact angles (9°) were observed for films prepared by acylation and with terminal pentyl groups; for one of these films, XR monitoring of film thicknesses showed a 1 Å increase in film thickness during 354 nm irradiation.